From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/2811 Path: news.gmane.org!not-for-mail From: Jens Gustedt Newsgroups: gmane.linux.lib.musl.general Subject: Re: [PATCH 1/3] protect some clobbered variables with volatile Date: Mon, 18 Feb 2013 01:13:51 +0100 Message-ID: <1361146431.29560.340.camel@eris.loria.fr> References: <1360535421.23424.467.camel@eris.loria.fr> <20130217175512.GE20323@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-/jO5jXqWKlH1oI8/DFJu" X-Trace: ger.gmane.org 1361146445 7420 80.91.229.3 (18 Feb 2013 00:14:05 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 18 Feb 2013 00:14:05 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-2812-gllmg-musl=m.gmane.org@lists.openwall.com Mon Feb 18 01:14:27 2013 Return-path: 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Cj15cu23XZI4/826Px/xqB37z547sPH374oOvnKTsOb+1zuCoImZARM8ZiLlKkXcWOcoFRJ+Do/CwFO4e2DEe+9Ti+ZXA8ny/cU+X4bMKRZxZIVEiqXI6/+NKuUzPHb7z40ovnX3zx+Ctuq38HyuqWG7Tu+A0AAAAASUVORK5CYII= X-Mailer: Evolution 3.2.3-0ubuntu6 Xref: news.gmane.org gmane.linux.lib.musl.general:2811 Archived-At: --=-/jO5jXqWKlH1oI8/DFJu Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hello Rich, AFAIR these both occurred when compiling with -flto. I would not trust the static analysis of the compiler at 100 % either, but this is just an argument to have the volatile in. The compiler is telling us that here he thinks that an optimization might hide a intermittent write, but that by the aliasing rules it would be OK to save a read. So better be careful and trust the compiler that he is willing to do bad things :) Maybe LTO is broken, yet, in that it might do some optimizations that it shouldn't. Or maybe this exposes possible problems that were previously hidden because the write was in a different compilation unit than the read. Who knows. In any case, the performance hit should be limited, and my personal preference would tend towards safety and calming down the compiler. Jens --=20 :: INRIA Nancy Grand Est :: http://www.loria.fr/~gustedt/ :: :: AlGorille ::::::::::::::: office Nancy : +33 383593090 :: :: ICube :::::::::::::: office Strasbourg : +33 368854536 :: :: ::::::::::::::::::::::::::: gsm France : +33 651400183 :: :: :::::::::::::::::::: gsm international : +49 15737185122 :: --=-/jO5jXqWKlH1oI8/DFJu Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iEYEABECAAYFAlEhcj8ACgkQD9PoadrVN+KpIQCeM4qW9yVvDciJQMojXDPWrpCW 7bIAn0j9h8wa2AvTP1/MtDvL1eKfjGT9 =gghs -----END PGP SIGNATURE----- --=-/jO5jXqWKlH1oI8/DFJu--